Worldwide it is estimated that there were around 600,000 cases and 325,000 deaths from head and neck cancer in 2012. Tobaccos and alcohol well established risk factors and are though to account for about 75% of head and neck cancers. The International Head and Neck Cancer Epidemiology (INHANCE) Consortium was established in 2004 to help clarify the role of lifestyle factors and investigate other aetiologic questions.

The aim of this overview paper was to summarise the findings of the INHANCE consortium to date.

Methods

The INHANCE consortium includes investigators of 35 studies who have pooled their data on 25,500 patients with head and neck cancer (i.e., cancers of the oral cavity, oro- pharynx, hypopharynx, and larynx) and 37,100 controls. Cases are included in the INHANCE consortium if their tumor had been classified by the original study as an invasive tumor of oral cavity, oropharynx, hypopharynx, oral cavity or pharynx not otherwise specified, larynx, or head and neck cancer unspecified according to the International Classification of Diseases for Oncology, version 2 [ICD- O-2], or the International Classification of Diseases, 9th [ICD-9; (30)] or 10th [ICD-10] Revision.

Most are case–control studies involving patients with head and neck cancer and a comparison group of controls without head and neck cancer; the other studies are case series-patients with head and neck cancers.

Findings

Among never alcohol drinkers, cigarette smoking was associated with an increased risk of head and neck cancer OR = 2.13, [95% CI; 1.53–2.98] and risks rose with frequency, duration, and pack-years of cigarette smoking.

A benefit to quitting smoking was evident in an INHANCE study as soon as 1–4 years after stopping tobacco smoking.

Alcohol drinking among persons who never used tobacco was linked to an increased risk but only among the heavier users (3 or more drinks per day vs. never drinkers) OR = 2.04, [95% CI; 1.29–3.21].

A study examined risks for cigarette smoking, pipe and cigar smoking each compared to persons who had not smoked that particular product, but controlled for the other products Increased risks of head and neck cancer were observed for

cigarettes (OR = 3.46, 95% CI 3.24–3.70),

cigars (OR = 2.54, 1.93–3.34),

pipes (OR = 2.08, 1.55–2.81).

For each of these behaviors, risks increase with frequency measured in numbers of cigarettes, cigars, and pipes, duration of use in years, and cumulative smoking (measured in the number of packs per day times number of years used, cigars per day times number of years used, and number of pipes smoked per day times number of years used).

Importantly, approximately twofold elevated risks were evident even in those with the least number of units smoked per day (1–10 cigarettes, cigars, or pipes).

Risks of head and neck cancer increased with number of ethanol-standardized units per week to:-

6.3 (95% CI 2.2–18.6) for wine-only drinkers with more than 30 drinks per week compared to people who never drank alcoholic beverages.

The effects of joint tobacco smoking and alcohol drinking on risk of head and neck cancer were greater than the multiple of the effects of the individual behaviors. These joint behaviours accounted for the majority of cases of oral cavity (64%), pharyngeal (72%), and laryngeal cancers (89%). However, these two behaviors jointly accounted for much less than that for cases that occurred at younger ages and for women.

Long duration of exposure to smoke involuntarily (more than 15 years) was associated with and increased risk, which was stronger for pharyngeal and laryngeal cancer than for oral cavity cancer

Low education was associated with an increased risk of head and neck cancer (OR = 2.50; 95% CI = 2.02 – 3.09) Overall one-third of the increased risk was not explained by differences in the distribution of cigarette smoking and alcohol behaviors; and it remained elevated among never users of tobacco and nondrinkers (OR = 1.61; 95% CI = 1.13 – 2.31)

Conclusions

Scientific findings from the INHANCE consortium have implications for causation, prevention, and clinical and public health policy, and publications based on INHANCE have provided more precise estimates of the fraction of head and neck cancers attributable to different risk factors and their combinations.

Comments

The pooling of data from a large group of studies from North America, (15 studies) Europe (13 studies) Latin America (3 studies) and Asia (3 studies) provides an opportunity to investigate a range of potential risk factors and the opportunity to investigate differences across studies and geographical areas. The authors highlight that the majority of studies included within the consortium are case-control studies or clinical case series so it may not be possible to determine if the exposure of interest occurred before diagnosis. Data for potential determinant and confounders was usually collected by questionnaires retrospectively so they may be some recall bias. In addition variations in questions may result in missing details between studies. Although overall INHANCE have generated useful data that have implications for causation, prevention, and clinical and public health policy

Derek Richards is the Director of the Centre for Evidence-based Dentistry, Editor of the Evidence-based Dentistry Journal, Consultant in Dental Public Health with Forth Valley Health Board and Honorary Senior Lecturer at Dundee & Glasgow Dental Schools. He helped to establish both the Centre for Evidence-based Dentistry and the Evidence-based Dentistry Journal. He has been involved with teaching EBD and a wide range of evidence-based initiatives both nationally and internationally since 1994.